In radio communication, layered modulation generally comprises a method whereby layering is achieved through combination with error correction or suchlike encoding, or a method whereby layering is achieved by modulation that physically places an information signal on a carrier separately from encoding.
The method disclosed in Patent Document 1 is an example of the latter type of layered modulation method. With the layered modulation method disclosed in Patent Document 1, a band for OFDM transmission is divided into a plurality of frequency blocks, carrier modulation is performed on each frequency block using a different modulation method, and OFDM modulation is performed via a combining circuit.
Specifically, an example of a conventional radio transmitting apparatus using the layered modulation method disclosed in Patent Document 1 will be described using FIG. 1 and FIG. 2. As shown in FIG. 1, transmitting apparatus 10 has switch 11, plurality of encoding sections 12-1 through 12-3, plurality of carrier modulation sections 13-1 through 13-3, combining circuit 14, IFFT (Inverse Fast Fourier Transform) section 15, and control information synchronization circuit 16.
Switch 11 sends transmission data to one of plurality of encoding sections 12-1 through 12-3. Plurality of encoding sections 12-1 through 12-3 encode transmission data using different encoding methods (for example, different coding rates). Plurality of carrier modulation sections 13-1 through 13-3 modulate encoded data using different modulation methods (for example, different M-ary modulation values).
Combining circuit 14 allocates subcarrier modulation signals S1, S2, and S3 output from carrier modulation sections 13-1 through 13-3 to corresponding frequency blocks. IFFT section 15 generates an OFDM signal by executing an IFFT on combining circuit 14 output and control information synchronization circuit 16 output. Control information synchronization circuit 16 outputs frequency block allocation information and a pilot signal.
FIG. 2 illustrates frequency block allocation by transmitting apparatus 10. Subcarrier modulation signal S1 output from carrier modulation section 13-1 is transmitted allocated to frequency block BL1 comprising a plurality of subcarriers. Similarly, subcarrier modulation signal S2 is transmitted allocated to frequency block BL2, and subcarrier modulation signal S3 is transmitted allocated to frequency block BL3.
In transmitting apparatus 10, changing the modulation method allocation to a frequency block for each OFDM symbol enables bit error rate degradation to be minimized even if only a specific frequency within the transmission band is greatly affected by multipath interference.    Patent Document 1: Japanese Patent Application Laid-Open No. HEI 7-321765    Non-Patent Document 1: S. B. Weinstein and P. M. Ebert, “Data Transmission by frequency-division multiplexing using the discrete fourier transform,” IEEE Trans. Commun. Technol., Vol. COM-19, pp. 624-634, October. 1971    Non-Patent Document 2: S. Lin and P. Yu, “A Hybrid ARQ Scheme with Parity Retransmission for Error Control of Satellite Channels,” IEEE Trans. Commun., vol. 30, no. 7, pp. 1701-1719, July 1982    Non-Patent Document 3: D. Chase, “Code combining—a maximum-likelihood decoding approach for combining an arbitrary number of noisy packets,” IEEE Trans. Commun., vol. 33, no. 5, pp. 385-393, May 1985    Non-Patent Document 4: J. Hagenauer, “Rate-compatible punctured convolutional codes (RCPC codes) and their applications,” IEEE Trans. Commun., vol. 36, no. 4, pp. 389-400, April 1988    Non-Patent Document 5: 3GPP TR 25.814 Physical Layer Aspects for Evolved Universal Terrestrial Radio Access v7.1.0    Non-Patent Document 6: 3GPP TS 25.212 Multiplexing and channel coding (FDD) v7.3.0    Non-Patent Document 7: 3GPP TSG RAN WG1 #42 R1-051167 Rate-compatible LDPC codes with low complexity encoder & decoder, San Diego, US, October, 2005